This invention relates to a welding robot controlling method, and more particularly to the method which provides an accurate weaving operation and automatic continuation of the weaving pattern throughout the full automatic welding.
As the method for realizing the weaving of a torch (a weaving operation) along a teaching line (welding line) of a robot, U.S. Pat. No. 4,188,525 and Japanese laid-open publication 56-89379 disclose one method, wherein for moving the center of the weaving exactly on the teaching line, repeating signals for the weaving operation are superposed on positional input signals given to positional servo circuits of respective drive axes of the welding robot. However, since this conventional method uses an oscillator and a signal memory element as repeating signals for the weaving operation, when the teaching line varies three-dimensionally at will, no accurate weaving patterns can be obtained. This can be readily understood by considering the nature of such repeating signals. Namely, since the repeating signals have a constant amplitude and frequency, it is not accurate in the case in which the teaching line of articulated robots, polar coodinate robots, or cylindrical coordinate robots is a straight line. As an example, in an articulate robot which moves the welding torch tip linearly as a combined movement of the drive axes, the linear movement of the torch becomes possible only with the combined control of the respective drive axes, and the positional input signals given to the positional servo circuit of the drive axes are not constant signals of either a ramp input or a step input, but are the complicated signals which vary every moment corresponding to the varying position of the robot.
To obtain a desired weaving pattern, the weaving repeating signals, which are to be superimposed on the complicated positional signals given to the respective drive axes, should vary in a complicated manner corresponding to the varying positions of the robot. The realization of such complicated varying of the weaving signals is not possible with a simple oscillator. On the other hand, to memorize such complicated weaving repeating signals as the positioning commands to the positional servo circuits of the respective drive axes utilizing the signal memory element requires an impractically large amount of storage capacity. A particularly novel method which improves these defects is proposed in U.S. Pat. No. 4,150,329. The proposed method consists in obtaining incremental displacements in three-dimensional space along X, Y and Z axes every constant period (in general, a short time of an order of milliseconds) by composing programming data which represent the principal movement along a plurality of teaching lines, and other programming data which represent a weaving movement (subordinate movement) without any displacement along the teaching lines. Although such prior art developments produce satisfactory weaving movement along one teaching line, the system is relatively complex and falls short of the present invention in providing flexibility and performance in continuous generation of weaving movements along a plurality of teaching lines.
When a robot locus which consists of a multiplicity of teaching lines is to be traced by the weaving operations, the teaching operation is required for seeking the amplitude and the frequency of the weaving repeating signals on each teaching line, whereby the operability of the teaching operation as a whole becomes extremely low.
Accordingly, it is an object of the present invention to provide a weaving control method which can overcome the above defects of the conventional methods.
The weaving control method of this invention provides that by controlling the three basic axes of a robot, a desired weaving operation is accurately executed on any teaching line.
The weaving control method of this invention is substantially characterized in that when a robot locus consisting of a multiplicity of teaching lines is to be traced by the weaving operation, by designating on the first teaching line three points which define the weaving pattern, an accurate weaving operation is obtained also on the successive teaching lines.